Nail Discoloration: Causes by Color

Nail discoloration by color

Yellow nails

Thick, yellow, brittle, crumbling toenails are the classic sign of fungal infection (onychomycosis). It usually starts at the tip or sides and spreads back. Debris builds up under the nail, and the nail may lift. It is common with age, athlete's foot, diabetes and in people who wear tight shoes or use communal showers.

Other causes of yellow nails include dark nail polish, smoking (nicotine stains fingernails on the hand that holds cigarettes), psoriasis, and rarely yellow nail syndrome, which causes slow-growing yellow nails with lymphedema and lung problems.

White nails and white spots

Small white spots or lines (leukonychia) usually follow minor knocks to the nail base and grow out over months. They are not caused by calcium or zinc deficiency, as commonly believed.

Whole-nail whitening can signal medical conditions:

• Terry's nails: mostly white with a narrow pink or brown band at the tip; linked to chronic liver disease, heart failure and diabetes, but also seen with aging.
• Half-and-half nails: white near the cuticle and reddish-brown at the tip; linked to chronic kidney disease.
• Muehrcke lines: paired white bands that do not move as the nail grows; linked to low protein levels.

Dark streaks and black nails

A brown or black stripe running lengthwise (longitudinal melanonychia) is common and harmless in many people with darker skin, often affecting several nails. Other harmless causes are pregnancy, medicines, injury and repeated friction.

However, a dark band can be subungual melanoma, a skin cancer under the nail. Warning signs:

• a single nail affected, especially the thumb or big toe
• a band that is new in adulthood, or getting wider or darker
• irregular or blurred borders, or several shades of brown or black
• pigment spreading onto the cuticle or skin around the nail (Hutchinson's sign)
• nail splitting or bleeding without injury

Any of these needs prompt assessment by a dermatologist.

Bruised nail

Bleeding under the nail (subungual hematoma) after a crush or stubbed toe causes a red, purple or black patch that hurts at first. It grows forward with the nail over months. If you do not remember an injury, or the patch does not move forward over 2 to 3 months, have it checked.

Green nails

Green or green-black discoloration usually comes from Pseudomonas bacteria growing under a nail that has lifted from its bed, especially in people whose hands are often wet. It is not dangerous. Keeping the nail dry and trimming the lifted part usually clears it; a doctor may prescribe antibacterial soaks or drops.

Blue nails

Nails turn bluish in the cold as vessels constrict. Blue nails that persist, especially with blue lips and breathlessness, mean low oxygen levels and need urgent care. Some medicines and silver exposure can permanently stain nails blue-gray.

Nail psoriasis

Psoriatic nails show pitting, yellow-brown "oil drop" patches, nail lifting and thickening. Nail psoriasis is common in people with skin psoriasis and more common in those with psoriatic arthritis.

How nail discoloration is diagnosed

A doctor or dermatologist will ask how long the change has been present, whether one or several nails are affected, about injuries, medicines, smoking, and other symptoms. They will examine the nails with a dermatoscope. Tests may include:

• nail clippings sent for fungal testing, since other conditions can look like fungus
• blood tests for anemia, liver, kidney or thyroid function
• nail biopsy of a suspicious dark band

Treatment

• Fungal nails: prescription oral antifungals (most effective) or medicated nail lacquers or solutions for mild cases. Treatment takes months because the nail must grow out: about 6 months for fingernails and 12 to 18 months for toenails.
• Bruised nail: cold compresses and elevation; a large painful hematoma can be drained by a doctor in the first day or two.
• Bacterial (green) nails: keep dry, trim lifted nail, topical antibacterial treatment.
• Psoriasis: topical treatments, injections into the nail fold, or systemic medicines.
• Staining: take a break from nail polish and use a base coat.
• Underlying conditions: treat anemia, liver, kidney or lung disease.
• Melanoma: surgery by a specialist.

Frequently asked questions

What does nail discoloration mean?

Most nail discoloration is harmless, from fungal infection, minor injury, nail polish or smoking. Some changes reflect health problems, such as white nails in liver or kidney disease, pale nails in anemia, or blue nails from low oxygen. A new dark streak can rarely be melanoma.

Why are my toenails turning yellow?

The most common cause of yellow, thickened toenails is a fungal nail infection. Other causes include dark nail polish, aging, psoriasis and rarely yellow nail syndrome. A doctor can confirm fungus by testing nail clippings before starting treatment.

When should I worry about a black line on my nail?

See a doctor if a dark line is new, in only one nail, getting wider or darker, has blurry or uneven edges, or if pigment spreads onto the skin around the nail. These can be signs of subungual melanoma. Bands in several nails in darker skin are usually harmless.

Do white spots on nails mean a deficiency?

Usually not. Small white spots are most often caused by minor knocks to the nail base and grow out over several months. They are not a reliable sign of calcium or zinc deficiency.

How long does nail discoloration take to go away?

It depends on the cause, but nails grow slowly. A fingernail takes about 6 months to grow out completely, and a toenail 12 to 18 months. Discoloration from injury or staining disappears as the nail grows. Fungal nails take months of treatment.